1. Field of the Invention
The present invention relates to a manufacturing method for preferentially-oriented oxide ceramics, and more particularly, to a manufacturing method for oxide piezoelectric ceramics. The present invention also relates to a piezoelectric element using the preferentially-oriented oxide ceramics, and a liquid discharge head, an ultrasonic motor, and a dust removing device, which utilize the piezoelectric element.
2. Description of the Related Art
Controlling the crystal orientation of the piezoelectric materials can effectively improve the piezoelectric performance of the piezoelectric materials. Because the piezoelectric property is an anisotropic physical property, the piezoelectric property of preferentially-oriented oxide ceramics is superior to that of randomly-oriented oxide ceramics.
As a method for manufacturing such preferentially-oriented oxide ceramics, a magnetic orientation method is disclosed in Sakka et al., “Journal of the European Ceramic Society”, 2008, vol. 28, pp. 935-942. According to this document, torque T(N·m) applied to a crystal in a magnetic field is expressed by the following equation (1).
                    T        =                  -                                    Δ              ⁢                                                          ⁢              x              ⁢                                                          ⁢                              VB                2                            ⁢              sin              ⁢                                                          ⁢              2              ⁢              θ                                      2              ⁢                              μ                0                                                                        Equation        ⁢                                  ⁢                  (          1          )                    
In the equation, B represents magnetic field intensity (N·A−1·m−1), μ0 represents vacuum magnetic permeability (N·A−2), θ represents an angle (degrees) between an axis of easy magnetization of the crystal and the magnetic field, and V represents particle volume (m3). This torque affects the crystal so that the axis of easy magnetization of the crystal and the magnetic field become parallel to each other.
Japanese Patent Application Laid-Open No. 2008-37064 discloses that tetragonal barium titanate as a typical piezoelectric material has (001) orientation in a magnetic field (tetragonal perovskite crystals are regarded as pseudo-cubic perovskite crystals in this specification unless otherwise noted). This means that the axis of easy magnetization of barium titanate is in <001> direction.
However, in Wada et al., “Japanese Journal of Applied Physics”, 1999, vol. 38, pp. 5505-5511, it is reported that when a voltage is applied in <111> direction in tetragonal perovskite piezoelectric materials, an engineered domain configuration is formed so that good piezoelectric property can be obtained. In other words, although a high performance piezoelectric element can be obtained by producing ceramics having (111) orientation, it is not easy to produce barium titanate ceramics having (111) orientation by the conventional magnetic orientation method because the axis of easy magnetization of tetragonal barium titanate is in <001> direction.
The conventional method has a problem in that a (111) orientation structure cannot be obtained by the magnetic orientation if the crystal has the axis of easy magnetization in <001> direction.